164
Atmel ATmega16/32/64/M1/C1 [DATASHEET]
7647K–AVR–12/13
Bit 6:5 – SJW1:0: Re-Synchronization Jump Width
To compensate for phase shifts between clock oscillators of different bus controllers, the controller must re-synchronize on any
relevant signal edge of the current transmission. The synchronization jump width defines the maximum number of clock cycles.
A bit period may be shortened or lengthened by a re-synchronization.
Bit 4 – Reserved Bit
This bit is reserved for future use. For compatibility with future devices, it must be written to zero when CANBT2 is written.
Bit 3:1 – PRS2:0: Propagation Time Segment
This part of the bit time is used to compensate for the physical delay times within the network. It is twice the sum of the signal
propagation time on the bus line, the input comparator delay and the output driver delay.
Bit 0 – Reserved Bit
This bit is reserved for future use. For compatibility with future devices, it must be written to zero when CANBT2 is written.
16.10.10 CAN Bit Timing Register 3 - CANBT3
Bit 7– Reserved Bit
This bit is reserved for future use. For compatibility with future devices, it must be written to zero when CANBT3 is written.
Bit 6:4 – PHS22:0: Phase Segment 2
This phase is used to compensate for phase edge errors. This segment may be shortened by the re-synchronization jump
Tphs2 = Tscl
× (PHS2[2:0] + 1)
Bit 3:1 – PHS12:0: Phase Segment 1
This phase is used to compensate for phase edge errors. This segment may be lengthened by the re-synchronization jump
width.
Tphs1 = Tscl
× (PHS1[2:0] + 1)
Bit 0 – SMP: Sample Point(s)
This option allows to filter possible noise on TxCAN input pin.
●
0 - the sampling will occur once at the user configured sampling point - SP.
●
1 - with three-point sampling configuration the first sampling will occur two
Tclk
IO clocks before the user configured
sampling point - SP, again at one
Tclk
IO clock before SP and finally at SP. Then the bit level will be determined by a
majority vote of the three samples.
‘SMP=1’ configuration is not compatible with ‘BRP[5:0]=0’ because TQ =
Tclk
IO.
If BRP = 0, SMP must be cleared.
Tsjw
Tscl
SJW[1:0]
1
+
()
×
=
Tprs
Tscl
PRS[2:0]
1
+
()
×
=
Bit
7654
3210
-
PHS22
PHS21
PHS20
PHS12
PHS11
PHS10
SMP
CANBT3
Read/Write
-
R/W
Initial Value
-
000
0000